I play around with different OS's, and I've found that to reduce the possibility of conflicts or errors, I just put each OS on its own HD.
HD's are so cheap now-a-days, that it just doesn't figure, to corrupt a good running HD with another OS.
I don't visit my Vista drive, but about once a week to keep it updated, but,
when I do, I just boot right into it from the boot menu in my BIOS.
NO, I don't change the boot order.....my bios actually has a Boot Menu, accessible by pressing the F11 key during the first few seconds of the boot-up process.
I have two totally different mobo's, made about five years apart and both have the built in boot menu and both are accessible by pressing the F11 key during boot-up.
I suspect that many folks have such a boot menu and don't even know it.
Anyway, in closing, I'd NEVER put two OS's on the SAME HD.
That can be a sure fire recipe for disaster. I've seen it happen, way too many times.
Y'all have a great day now, Y'hear?
Shadow